1. Field of the Invention
The present invention relates to an electromagnetic wave detector and an electromagnetic wave detector array, and more particularly to an electromagnetic wave detector and an electromagnetic wave detector array using single or multilayer graphene as a photodetecting layer.
2. Description of Related Art
In conventional electromagnetic wave detectors, semiconductor materials are used for photodetecting layers. However, because the semiconductor material has a band gap, only light having larger energy than the band gap can be detected, and therefore, the semiconductor cannot be said to be optimum for an electromagnetic wave detector. Therefore, attention has been focused on graphene as a next-generation light detection material. Graphene is a monoatomic layer of a two-dimensional carbon crystal, and single-layer graphene has a very small thickness of 0.34 nm which is equivalent to one carbon atom. Graphene has a carbon atom in each chain arranged in a hexagon shape, and is reported to be able to increase carrier mobility to ten thousand cm2/Vs or more. Researches and developments of using graphene for wirings of transistor channel layers and LSI are also being progressed. By utilizing such unique electric properties of graphene, there has been recently proposed the use of graphene, not only as materials of high-speed devices, LSI wirings, and electrodes, but also as materials of photodetecting layers of electromagnetic wave detectors.
For example, JP 2013-502735 A discloses an electromagnetic wave detector that has a graphene channel layer deposited on a gate oxide film on a substrate, and has source and drain contact regions formed on both ends on the graphene. It is described that the graphene of the photodetecting layer of the electromagnetic wave detector is zero or a very small band gap material, and can detect light in a broad bandwidth. Further, it is described that a carrier 1 of graphene in a high electric field is ten times to a hundred times of the carrier transfer rate in a conventional semiconductor.
However, because a photoabsorbing layer formed of only graphene has a very low optical absorption rate of a few percent, the photoabsorbing layer cannot effectively acquire optical information as an electromagnetic wave detector. Further, the conventional electromagnetic wave detector using graphene does not have a function of detecting polarization of incident light. Therefore, in order to detect specific polarization, it has been necessary to provide a polarization filter or the like on a light incident surface.